In deep level mining operations cold water is used extensively to cool underground work places. The water is chilled on surface and is piped to underground locations where the cooling is required. The resultant hot water is then pumped back to surface where it is again cooled and the cycle is repeated. Because of the water pressure head which exists at mine depths of thousands of meters the hot water pumping costs are enormous and it is not uncommon to employ power recovery systems such as Pelton wheel generating sets which use the cold water head to generate electricity to supplement the energy required for operating the pumps.
To minimise the above pumping and related costs, underground chamber water transfer systems were experimented with in South African mines in the early 1970's. The principle of operation of these systems is the charging of a chamber with a low pressure driven liquid or slurry from the underground mine workings and then to discharge the water or slurry from the chamber through a pipeline to surface by means of high pressure drive cold water from surface. The cold water is then discharged from the chamber to a cold water tank by the reintroduction of hot water into the chamber. The cold water from the tank is used for the cooling of the mine workings with the so heated water being pumped to a hot water tank for transmission through the chamber back to surface.
Over the years single, double and triple type chamber systems have been experimented with with typical examples of these being those disclosed in South African patent Nos. 82/0078, 87/3617, 87/4735 and U.S. Pat. No. 4,991,998. The double chamber systems were not reliable and the continuity of delivery of the driven liquid from the systems was problematical and could not be guaranteed. Flow interruptions in the systems caused, among other problems, severe water hammer. In practice the high pressure pipe lines to and from the underground system would have a nominal bore of about 200 mm and would need to cope with 120 bar water pressure. Water hammer in such a system would at the very least be traumatic. The more continuous flow achieved with the three chamber systems reduced problems which existed in the two chamber systems and, unlike the two chamber systems, were developed to actual use. However, even the three chamber systems have problems and are not totally reliable.
The most common problems connected with all known fluid transfer systems of the above type are:
The extremely large and costly underground excavations which are required to accommodate the pipe chamber feeders of the systems which are made from heavy piping which is as long as 100 m and which is folded into the form of a U. PA1 Water hammer in all of these systems which remains an ongoing problem. PA1 The control valves for operating the pipe feeders; with the vast majority of these valves being expensive and difficult to control high pressure gate valves which require use of external pressure balancing valves. As the valve switching is time or volume dependent they are responsible for a phenomenon known as "system creep" which results in the interface between the hot and cold water in the chambers creeping one way or the other over prolonged use of the system which is difficult to detect and eventually results in a total break down of the efficiency of the system. PA1 In many of the known fluid transfer systems the transfer chambers do not include any means for separating the hot from the cold water in the chamber and although a natural barrier appears to exist between the two liquids in normal operation of the system any deviation in the system timing will cause the hot water to temperature contaminate the cold water adversely to affect the mine cooling aspect of the system. This problem becomes highly aggravated in systems in which the driven liquid is a slurry. PA1 The thermal efficiency of the known pipe feeder systems is low as the internal surface area of the long pipe chamber feeders is very large and in each cycle of operation of the chamber becomes heated by the incoming hot water and then again cooled by the incoming cold water to result in a significant increase in the temperature of the cold water which is displaced from the chamber to the cold water tank.